#include <STC15F2K60S2.H>
#include "intrins.h"
#define DELAY_TIME 5

//总线引脚定义
sbit sda = P2^1;  /* 数据线 */
sbit scl = P2^0;  /* 时钟线 */

static void I2C_Delay(unsigned char n)
{
    do
    {
        _nop_();	
    }
    while(n--);      	
}
//
void I2CStart(void)
{
    sda = 1;
    scl = 1;
	I2C_Delay(DELAY_TIME);
    sda = 0;
	I2C_Delay(DELAY_TIME);
    scl = 0;    
}

//
void I2CStop(void)
{
    sda = 0;
    scl = 1;
	I2C_Delay(DELAY_TIME);
    sda = 1;
	I2C_Delay(DELAY_TIME);
}

//
void I2CSendByte(unsigned char byt)
{
    unsigned char i;
	
    for(i=0; i<8; i++){
        scl = 0;
		I2C_Delay(DELAY_TIME);
        if(byt & 0x80){
            sda = 1;
        }
        else{
            sda = 0;
        }
		I2C_Delay(DELAY_TIME);
        scl = 1;
        byt <<= 1;
		I2C_Delay(DELAY_TIME);
    }
	
    scl = 0;  
}

//
unsigned char I2CReceiveByte(void)
{
	unsigned char da;
	unsigned char i;
	for(i=0;i<8;i++){   
		scl = 1;
		I2C_Delay(DELAY_TIME);
		da <<= 1;
		if(sda) 
			da |= 0x01;
		scl = 0;
		I2C_Delay(DELAY_TIME);
	}
	return da;    
}

//
unsigned char I2CWaitAck(void)
{
	unsigned char ackbit;
	
    scl = 1;
	I2C_Delay(DELAY_TIME);
    ackbit = sda; 
    scl = 0;
	I2C_Delay(DELAY_TIME);
	
	return ackbit;
}

//
void I2CSendAck(unsigned char ackbit)
{
    scl = 0;
    sda = ackbit; 
	I2C_Delay(DELAY_TIME);
    scl = 1;
	I2C_Delay(DELAY_TIME);
    scl = 0; 
	sda = 1;
	I2C_Delay(DELAY_TIME);
}

unsigned char PCF8591_Adc(void) 
{ 
 unsigned char temp; 
 I2CStart(); 
 I2CSendByte(0x90);
 I2CWaitAck();
 I2CSendByte(0x43); // 允许 DAC，ADC 通道 3 0x43读电压值,0x41光敏电阻
 I2CWaitAck();
 I2CStart(); 
 I2CSendByte(0x91); 
 I2CWaitAck();
 temp = I2CReceiveByte();
 I2CSendAck(1); 
 I2CStop(); 
 return temp; 
} 